1. Field of the Invention
This invention relates to radio communication systems and methods, and more particularly relates to systems and methods for improving the directionality of radio receivers. Even more specifically, this invention relates to an interference cancelling system and method for achieving effectively narrow beamwidth without the use of large antenna systems.
2. Description of the Prior Art
In order for a radio receiver system to achieve high directionality, large antennas or antenna arrays which are either active, i.e., adaptive, or passive, are currently used. For an antenna or a passive antenna array, the half power bandwidth is typically equal to about 50.multidot.X/L to about 80.multidot.X/L, where X is the wavelength of the radio waves received by the system, and L is the dimension of the antenna in the plane of the beamwidth. Accordingly, the antenna dimensions may become quite large for narrow beamwidths.
Radio receiver systems employing adaptive antenna arrays as well as interference cancellation systems usually require N+1 antennas to cancel N signals without affecting a desired signal. N control loops in the cancellation systems of such radio receiver systems are also required. Accordingly, high directionality is achieved in such conventional radio receivers only with large antennas or antenna arrays.